1. Field of the Invention
The present invention relates to a display system for a controller for controlling a machine, in which a display device and the controller are connected to each other by a network.
2. Description of the Related Art
Already known is a system in which a controller for controlling a machine tool or the like and a personal computer used as a display device are connected to each other by a network. For example, there is a system (see Japanese Patent Application Laid-Open No. 2003-5812) in which screen data to be displayed on a display device of a numerical controller can be displayed on a screen of a personal computer that is connected by a network. In another known system (see Japanese Patent Application Laid-Open No. 2-53106), a numerical controller and a computer are connected to each other by a network so that the computer can monitor a display screen of the numerical controller without the use of a display control section.
Also known is a system (Japanese Patent Application Laid-Open No. 2002-111680) in which a controller, a display device for controller, and a host device are connected to one another by a network. In this system, the display device for controller makes a conversion between a data representation format in a data column transferred by communication between the host device and itself and a data representation format in a data column transferred by communication between the controller and itself, thereby relaying the communication between the controller and the host device.
According to the conventional system in which the controller and the display device are connected by the network, display data of the controller can be displayed only during normal operation in which the controller is normally initialized and a communication function is performed. Therefore, the display data cannot be displayed at the time of initialization of the controller or in case of system alarm.
If the network conditions are poor, although the controller is in the normal operation, moreover, error detection with a normal communication time-out function for the communication function is time-consuming, and a function to check the communication status is unsatisfactory. Accordingly, it takes time to be allowed to conclude that the display device is not operating correctly. Thus, maintenance work to cover malfunction of the controller or solve network problems requires a separate display device that is connected by video signals or the like.